Solar power generation involves harvesting solar radiation and converting it to usable energy, such as direct current (DC) electricity. Solar energy may be collected directly onto photovoltaic cells, such as in flat panel technology, or may undergo various stages of refraction and reflection, such as in solar concentrators, before impacting a photovoltaic solar cell. Solar concentrators use vastly decreased amounts of costly photovoltaic material by concentrating incoming solar radiation onto a surface area which is much smaller than that of the entry window area of the overall concentrator unit. Thus, the efficiency of a solar concentrator unit is affected not only by the amount of solar energy captured by the unit, but also by the ability of the unit to accurately deliver the concentrated light to the relatively small photovoltaic cell. Efforts to increase the efficiency of solar concentrators include using solar tracking systems to maximize the intensity of incoming radiation, and modifying the materials used to fabricate components in order to enhance reflective and refractive properties. In addition, solar concentrator efficiency has been addressed by changing the design of individual components to increase acceptance angles. For instance, the shapes of entry window lenses and the wall profiles of mirrors used for collecting solar radiation have been varied widely in efforts to optimize solar concentration.
One type of solar concentrator, disclosed in U.S. Patent Publication No. 2006/0266408, entitled “Concentrator Solar Photovoltaic Array with Compact Tailored Imaging Power Units” utilizes a primary mirror and a secondary mirror to reflect and focus solar energy onto a non-imaging concentrator which delivers the energy to a solar cell. A similar type of solar concentrator, disclosed in U.S. Patent Publication No. 2006/0207650 and entitled “Multi-Junction Solar Cells with an Aplanatic Imaging System and Coupled Non-Imaging Light Concentrator,” uses a solid optic, out of which a primary mirror is formed oil its bottom surface and a secondary mirror is formed in its upper surface. Solar radiation enters the upper surface of the solid optic, reflects from the primary mirror surface to the secondary mirror surface, and then enters a non-imaging concentrator which outputs the light onto a photovoltaic solar cell. For both of these solar concentrators, variances in incoming radiation angle are greatly multiplied by having light reflect off of primary and secondary mirrors. For instance, a 1° change in incoming radiation angle may result in a 25° change in angle at the non-imaging concentrator.
Thus, the ability of the non-imaging concentrator to accept a wide range of incoming light angles can increase the efficiency of a solar concentrator system. It is desirable to design a non-imaging concentrator having an improved acceptance angle while maintaining its performance.